Radio direction finder



July 29, 1952 'J. D. BRAILSFORD EI'AL 2,605,465

RADIO DIRECTION FINDER Filed Feb. 23, 1949 A TEhEfigRONIC 6 SM c l CIRCUIT 1 18 RECTANGULAR WAVE FORM OUTPUT TERMINAf FILTER 12% 9 FILTER T r FILTER men TENSION souracs 4 v I). 7/ I low VOLTAGE 2 Z D-c. .sourzcs l FILTER Patented July 29, 1952 UNITED STATES PATENT-crews RADIO DIRECTION FINDER .l'oseph Douglas Brailsford and Eric Burnett Vass, Chelmsford, England, assignors to Marconis Wireless Telegraph Company Limited, London, England, a company of Great Britain Application February 23, 1949, Serial No. 77,922

' In Great Britain March 4, 1948 This invention relates to radio direction finders and more specifically to radio direction finders of the so-called switched cardioid type. In this well known type of radio direction finder the receiver proper is fed with the combined signals from a directional aerial system of variable directivity (usually, though not necessarily a loop aerial) andfrom a non-directional aerial system (usually an open aerial) the sense of combination being reversed at, a predetermined frequency (the so-called cardioid switching frequency) in .synchronism with a corresponding switching of the output circuit of said receiver so that an indicator fed with said switched output will give an indication of course error. Usually the indicator is a central zero instrument which deflects to left or right in dependence on the sense of the course error and reads zero when the incoming signal direction and the orientation of the .directivity of the directional aerial or system coincide.

ihe invention seeks to provide-improved and simplified means for providing or controllingthe necessary input and output switching in a radio component for providing an A. C. output which is at the cardioid switching frequency and is available for such purposes as operating indicator repeaters and/or automatically controlling the directivity of the directional aerial system in such manner as to provide a simple, automatic, self-orienting direction finder.

- 1 According to this invention the required synchronous input and output switching in a radio direction finder of the switched cardioid type is effected by means including an electro-magnetic vibrator the armature of which actuates amakeand-break. contact forming part of [a network whereby asteady potential is transformed into an approximatelyrectangular wave form which is then employed for effecting one of the required switching operations electronically, said armature also actuating. a second make-and-break contact which is employed as a mechanical switch'foreffecting the other of the required switching operations.

Preferably the armature alsoactuates further contacts forming part of a second network wherefrom the receiver proper.

2 Claims. (Cl. 343-117).

by a steady potential is transformed into an alternating potential which is thusavailable for operating indicator repeaters of known form e. g. so-called Selsyn repeaters. Preferably, however, thisAC. potential is utilized in addit1on (or instead) to provide one phase input to a VG-P11358011 similarmotor which is employed for orienting the directivity ofthe loopor equivalent aerial system of the direction finder, another phase input to said motor being provided With this arrangement the two phase inputs will, of course, be of the same frequency (the cardioid switching frequency) and-the-motor will therefore automatically rotate the loop, or'its equivalent, to the oncourse position an'd will then stop since, in this position, the motor phase input from the receiver disappears.

Preferably the secondm'ak-and-break contact actuated by the armature is employed to constitute mechanical switching means, actuated at the cardioid switching frequency, for securing response of the indicator substantially only for alternate. half waves of said frequency.

The invention is illustrated in the accompanying drawing which shows in simplified diagrammatic manner, one embodiment thereof.

Referring to the drawing, in the embodiment therein illustrated there is employed an electromagnetic vibrator of the kind commonly employed, for example, in radio receivers for use on automobiles for deriving high tension anode potential from a low voltage source constituted for exampleby the automobile lighting and starting battery. The operating coil 1 of the vibrator is shunted by a; surge limiting resistance 2 and is included as in the usualway ina circuit extendmg between one terminal 3 of a suitable low voltage-D. C. source (whose other terminal 4 is earthed) and earth, said circuit comprising inseries a smoothing-filter 5, the coil I itself; an operating contact fi on .to which the vibratory armature 7 ,makes when released by the coil,

. anda portion of the said armature.

A first contact 8 adjacent the armature is connected through a suitable filter 9 and resistance It in series to the live terminal I l of a high tension source (whose other terminal is earthed and 'will be seen that when the armature 1 makes to the contacts the potential at the adjacent side of' the condenser l2 will fall abruptly to able purpose, is employed, in any convenient manner known per se, to control any suitable known electronic switching circuit represented by the rectangle It for efiecting cardioid switching at the input side of the receiver 11, i. e. for

reversing the sense of combination of the inputs from the direction and non-directional aerials' indicated at L and A respectively. As these input circuits and the circuit details at [6 and H form per se no part of the invention and may be as known per se, no further description or illustration is necessary herein, the rectangular switching wave being indicated simply as fed to the circuit I6 over the lead IS.

The armature I also co-operates with a second adjacent contact l9 which is connected through a suitable filter and the secondary 2| of a transformer to one terminal of a central zero left-right indicator instrument 22 the other terminal of which is earthed. The primary 23 of this transformer is fed with L. F. output from the direction finding receiver II. It will then be seen that the contact [9 in conjunction with the armature I thus provides receiver output switching at the cardioid switching frequency in such manner as to secure response of'the indicator substantially only for alternate half waves of the said switching frequency, said; indicator being unresponsive at other times.

In addition to the contacts already mentioned the operating contact 6 and the first and second contacts 8 and l9the armature 1 is also associated With two. additional contacts 23, 24 which may be termed the third and fourth contacts and between which said armature 1 vibrates. These contacts are connected respectively to the opposite ends of a transformer primary 25 having a center tap 26 connected to the live terminal 3 of the low voltage D. C. source through the filter 5 already mentioned. The said contacts 23, 24 are also connected through respective spark suppressing condensers 2'1, 28 in series witha common resistance 29 to earth. It will be seen that with this arrangement A. C. voltage at thecardioid switching frequency will appear across the secondary30 of the transformer and. this voltage is made available at terminals 3| for operating Selsyn repeaters or the like (not shown) and/or for driving a loop rotating motor and for such other purposes as may be required. Preferably, where an automatic self-orienting direction finder is required this A. C. voltage is used as illustrated to provide one phase input to a two phase loop rotating electric motor the other phase drive of which is derived from the receiver output. Asshown the motor 32 which has one phase winding 3 3 energised from the secondary 30 and the other phase winding 34 fed from the receiver l1, rotates the frame aerial A via a mechanical drive conventionally indicated by the broken line 35. Since the energization of winding 34 will become zero when the loop A is on course, for in this condition the receiver I! gives a null orz'ero output, the loop will be automatically rotated to'the on course position and then stop. It will be noted that an important advantage obtained with this arrangement is that, since the A. C. voltage provided by the vibrator is, in eifect, an independent A. C. rigorously in synchronism with the cardioid switching frequency, bearing errors caused by the introduction of components of cardioid switching frequency into circuits other than those intended therefore are avoided.

We claim:

1. In a radio direction finder of the switched cardioid type having synchronous input and output circuit switching operations, the combination of an electromagnetic vibrator having a vibratory armature, an approximately rectangular wave form producing network including a steady potential source, and a first make-and-break contact actuated by said armature, an electronic switching circuit connected to effect one of said switching operations, a circuit connecting said network with said switching circuit to control the same in accordance with the approximately rectangular wave forms from said network, and a second make-and-break contact actuated by the same armature and connected as a mechanical switch to efiect the other of said switching operations.

2. In a radio direction finder of the switched cardioid type having synchronous input and output circuit switching operations, the combination of an electromagnetic vibrator having a vibratory armature, an approximately rectangular wave form producing network, a direct current source connected through said vibratory armature, a first make-and-break contact actuated by said armature, an electronic switching circuit connected to effect one of said switching operations, a circuit connecting said network with said switching circuit to control the same in accordance with the approximately rectangular wave forms from said network, and a second makeand-break contact actuated by the same armature for producing an alternating potential from said direct current source for effecting the other of said switching operations.

3. A radio direction finder of the switched cardioid type as set forth in claim 2 in which said second make-and-break contact connects with opposite terminals of the primary winding of a transformer system having a mid tap return to said direct current source and a secondary winding coupled with said primary winding for exciting one phase of a two phase motor, and means controlled by said first make-and-break contact for controlling the other'phase of said two phase motor. I

4. A radio direction finder of the switched cardioid type as set forth in claim 2 which includes a loop antenna driven by a two phase motor, a radio receiver connected with said loop antenna, a connection from said first make-and-break contact through said radio receiver for supplying alternating current to one phase of said two phase motor and a connection from said second makeand-break contact with the other phase of said two phase motor for supplying alternating current-thereto at the cardioid switching frequency.

5. A radio direction finder of the switched cardioid type as set forth in claim 2 which includes a loop antenna driven by a two phase motor, a

radio receiver connected withsaid loop antenna,

, a right-left indicator connected with the output of said radio receiver, a connection from said first make-and-break contact with said right-left indicator forsupplying alternate half waves to said indicator at the cardioid switching frequency, a connection from said first make-andloreak contact through said radio receiver for supplying alternating current to one phase of said two phase motor and a connection from said second make-and-break contact with the other phase of said two phase motor for supplying alternating current thereto at the cardioid switching frequency.

6. Radio direction finder apparatus as set forth in claim 2 including indicator repeater means and connections for applying said alternating potential as operating potential to said indicator repeater means.

7. Radio direction finder apparatus as set forth in claim 2 including an electric motor having a plurality of phase windings said motor being coupled to the directional aerial system of said direction finder for orienting the directivity of the same, means providing one operating phase input for said motor from the receiver of said direction finder, and means providing another operating phase input for said motor from said alternating potential.

6 8. Radio direction finder apparatus as set forth in claim 1 in which said mechanical switch is actuated at the cardioid switching frequency, for securing response of the indicator of the radio direction finder substantially only for alternate half waves of said frequency.

JOSEPH DOUGLAS BRAILSFORD. ERIC BURNETT VASS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,054,160 Leib Sept. 15, 1936 2,216,708 Kolster Oct. 1, 1940 2,276,235 Lamb Mar. 10, 1942 2,279,021 Cooper et a1 Apr. 7, 1942 2,310,052 Bartholy Feb. 2, 1943 2,360,810 Carlson et a1. Oct. 17, 1944 

